I use tmux splits (panes). Inside one of these panes there's a Vim process, and it has its own splits (windows).

In Vim I have key bindings C-h/j/k/l set to switch windows in the given direction. (Vim default mappings for windows switching are the same, but prefixed with C-W.) I'd like to use the same keystrokes for switching tmux panes.

An extra goal that I've solved with a dirty hack is to toggle between last active panes with C-\.

This started out as a config that was mostly pulled from one of the first Google results for fmux.conf, and one of the first results for tmux. But now weighing in at 150 lines it is a force to be reckoned with.